1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer, and an image forming method.
2. Description of the Related Art
There has been known an image forming apparatus having a post-processing apparatus connected to a sheet discharge opening of the image forming apparatus to carry out various types of post-processing including stapling, punching, folding, and book binding for sheets on which the image forming apparatus has completed image formation.
When the post-processing apparatus is made to carry out the post-processing, it is necessary to keep long enough the intervals which are constant and at which sheets are discharged from a main body of the image forming apparatus, or to temporarily pool or buffer the discharged sheets on a stage prior to a post-processing section of the post processing apparatus (a buffering function), so as not to disturb or hinder the post-processing carried out by the post-processing section. Among inexpensive image forming apparatuses with a low productivity, there is a type which is adapted to widen the intervals at which sheets are discharged, but many image forming apparatuses are generally provided with the buffering function so as to increase the productivity, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H11-130328 and Japanese Laid-Open Publication (Kokai) No. 2001-097631.
However, if the main body of the image forming apparatus or the post-processing apparatus incorporates the buffering function, a space occupied by a buffering section, a drive mechanism used for the buffering section, and other component parts pose a problem that the main body of the image forming apparatus or the post-processing apparatus increases in size. This also leads to an increased cost.